1. Field of the Invention
The present invention relates to a new print head, a manufacturing method therefore, and a printer.
2. Description of the Related Art
Conventionally, such print heads are known in which ink-pressurizing cells, which are individually provided with heating elements, are covered by a nozzle-formed member, in which small ink-ejection nozzles are formed. When the heating elements are rapidly heated, bubbles of ink vapor (ink bubbles) are generated, and ink drops are ejected from the ink-ejection nozzles due to pressures applied by the ink bubbles.
Such a print head normally has a construction shown in FIGS. 34 and 35.
A print head a includes a substrate member d which is provided with heating elements c and which defines side surfaces and one end surface of ink-pressurizing cells b. The substrate member d is constructed by forming the heating elements c on a surface of a semiconductor substrate e formed of silicon, etc., and laminating a barrier layer f on the semiconductor substrate e at the same side as the side at which the heating elements c are deposited. The barrier layer f defines side surfaces of the ink-pressurizing cells b; in other words, it serves as side walls of the ink-pressurizing cells b. The barrier layer f is formed of, for example, a dry film which is curable by light exposure, and is constructed by laminating the dry film over the entire surface of the semiconductor substrate e, on which the heating elements c are formed, and removing unnecessary parts by a photolithography process. Accordingly, the substrate d is completed.
Then, a nozzle-formed member g is laminated on the barrier layer f of the substrate member d. The nozzle-formed member g is provided with ink-ejection nozzles h, which are aligned relative to the heating elements c formed on the substrate member d.
Accordingly, the ink-pressurizing cells b, of which end surfaces are defined by the substrate member d and the nozzle-formed member g, and side surfaces are defined by the barrier layer f, are formed. The ink-pressurizing cells b are linked with an ink passage i, and are provided with the ink-ejection nozzles h which oppose the heating elements c. The heating elements c in the ink-pressurizing cells b are electrically connected to an external circuit via conductors (not shown) deposited on the semiconductor substrate e.
Normally, a single print head includes hundreds of heating elements c and ink-pressurizing cells b containing the heating elements c. The heating elements c are selectively heated in accordance with a command issued by a control unit of a printer, and ink drops are ejected from the corresponding ink-ejection nozzles h.
In the print head a, the ink-pressurizing cells b are filled with ink supplied via the ink passage i from an ink tank (not shown) which is combined with the print head a. When a current pulse is applied to one of the heating elements c for a short time such as 1 to 3 μs, the heating element c is rapidly heated, and a bubble of ink vapor (ink bubble) is generated at the surface thereof. Then, when the ink bubble expands, a certain volume of ink is pushed ahead, and the same volume of ink is ejected out from the corresponding ink-ejection nozzle h as an ink drop. The ink drop, which is ejected from the ink-ejection nozzle h, adheres (lands on) to a print medium such as a piece of paper, etc.
The above-described print head a is usually used for a serial head which includes a plurality of head chips. A single head chip is formed by laminating a single substrate member, in which a plurality of ink-pressurizing cells and heating elements are formed, on a single nozzle-formed member, and a plurality of head chips are arranged in a direction perpendicular to the feed direction of the print medium.
When the print head a is used, it is moved in the direction perpendicular to the feed direction of the print medium and prints a line. Then, the print medium is moved in the feed direction and the next line is printed.
In the above-described print head a, characteristics of ink drop ejection are affected by positional relationships between the heating elements c (the ink-pressurizing cells b) and the ink-ejection nozzles h. When the heating elements c (the ink-pressurizing cells b) and the ink-ejection nozzles h are greatly displaced, the ejection speed may be reduced and the ejecting direction may be changed. Furthermore, it may even be impossible to eject ink drops. Accordingly, displacements between the heating elements c (the ink-pressurizing cells b) and the ink-ejection nozzles h lead to a degradation of the printing quality, and thus are a large problem.
Generally, heating processes are necessary for manufacturing the print head a. For example, after the barrier layer f is formed on the semiconductor substrate e and the nozzle-formed member g is laminated on the barrier layer f, a heat curing process for curing the barrier layer f and fixing the nozzle-formed member g is performed at a high temperature. In addition, another high-temperature curing process is performed to provide ink resistance to the barrier layer f, which is formed of dry film resist.
As described above, heating processes are necessary for manufacturing a print head. Coefficient of linear expansion of silicon, which is normally used for forming the semiconductor substrate e, is 2.6×10−6, and that of nickel, which is normally used for forming the nozzle-formed member g, is 13.4×10−6. Accordingly, the coefficients of linear expansion of silicon and nickel differ by approximately one order of magnitude.
When two materials having extremely different coefficients of linear expansion are laminated together in a heating process, relative displacement occurs due to the difference in shrinkage rates. Such a displacement varies in accordance with the difference in the coefficients of linear expansion between the members that are laminated together, and is increased as the difference becomes larger.
With reference to FIG. 36, at position (a), the heating element c (the ink-pressurizing cell b) and the ink-ejection nozzle h are aligned. However, at position (b), which is apart from position (a), the ink-ejection nozzle h is displaced relative to the heating element c (the ink-pressurizing cell b), and at position (c), which is farther apart from position (a), the ink-ejection nozzle h is completely displaced, even from the ink-pressurizing cell b. Such a displacement increases along with the size of the members which are laminated together. When the heating element c (the ink-pressurizing cell b) and the ink-ejection nozzle h are displaced relative to each other (see FIG. 36, position (b)), the ejecting direction is changed. In addition, when the displacement therebetween is increased still further (see FIG. 36, position (c)), it becomes impossible to eject ink.
In the printer market, it is required to increase the printing speed, and one approach to satisfy this requirement is to increase the number of nozzles from which ink is ejected. When the resolution of a printer is maintained and the number of nozzles is increased, the size of a print head is also increased. Thus, the influence of the displacements between the heating elements c (the ink-pressurizing cells b) and the ink-ejection nozzles h, which occur due to the difference in coefficients of linear expansion, is also increased. In addition, in large print heads such as line heads, etc., there is a large problem in that the displacements between the heating elements c (the ink-pressurizing cells b) and the ink-ejection nozzles h become relatively large.
In addition, the conventional print head includes a plurality of head chips that are individually constructed, and the ink passages and the nozzle-formed members contained in the head chips are separately installed. Accordingly, the conventional print head has a complex structure for supplying each of the head chips with ink.
Furthermore, since a single head chip is constructed on a single nozzle-formed member, the printing characteristics are degraded due to the dimensional errors of the head chips, displacements of the head chips which occur when the head chips are arranged, etc.
Short length of the head chips is another cause of the degradation of the printing characteristics.
Since the head chips are manufactured by forming heating elements on a semiconductor substrate, that is, on a circular semiconductor wafer, it is difficult to form long substrate members. When the length of the substrate members is increased, yield is reduced and manufacturing cost is increased. Accordingly, it is difficult to increase the length of the substrate members. However, when the heating elements are formed on the substrate members having a short length, it is difficult to make sizes, thicknesses, etc., of the heating elements formed in the different substrate members the same.
As a result, when a plurality of head chips are arranged, the characteristics of ink drop ejection, and more specifically, the size of the ink drops, cannot be made uniform at all of the head chips.
When such head chips are merely arranged on one line, images printed by the adjacent head chips appear differently. Accordingly, there is a problem in which print mottling occurs.